Gasification of plastic waste as waste-to-energy or waste-to-syngas recovery route

The disposal of plastic solid waste (PSW) has become a major worldwide environmental problem. New sustainable processes have emerged, i.e. either advanced mechanical recycling of PSW as virgin or second grade plastic feedstock, or thermal treatments to recycle the waste as virgin monomer, as synthetic fuel gas, or as heat source (incineration with energy recovery). These processes avoid land filling, where the non-biodegradable plastics remain a lasting environmental burden. Within the thermal treatments, gasification and pyrolysis gain increased interest. Gasification has been widely studied and applied for biomass and coal, with results reported and published in literature. The application to the treatment of PSW is less documented. Gasification is commonly operated at high temperatures (> 600℃ to 800℃) in an air-lean environment (or oxygen-deficient in some applications): the air factor is generally between 20% and 40% of the amount of air needed for the combustion of the PSW. Gasification produces mostly a gas phase and a solid residue (char and ashes). The use of air introduces N2 in the product gases, thus considerably reducing the calorific value of the syngas, because of the dilution. The paper will review the existing literature data on PSW gasification, both as the result of laboratory and pilot-scale research. Processes developed in the past will be illustrated. Recently, the use of a sequential gasification and combustion system (at very high temperatures) has been applied to various plastic-containing wastes, with atmospheric emissions shown to be invariably below the legal limits. Operating results and conditions will be reviewed in the paper, and completed with recent own lab-scale experimental results. These results demonstrate that gasification of PSW can be considered as a first order reaction, with values of the activation energy in the order of 187 to 289 kJ/mol as a function of the PSW nature.

Study on the microwave-assisted extraction of polyphenols from tea

This study demonstrated a promising method for quickly extracting tea polyphenol(TP)by microwaveassisted extraction(MAE)technology.Some influential parameters,including MAE temperature,microwave power,concentration of extraction solvent,MAE time and the solid/liquid ratio,were investigated.The optimum condition of MAE was obtained by dual extraction with 60%ethanol(v/v)and the solid/liquid ratio 1:12 g/mL at 80℃ for 10 minutes under the microwave power 600W.The yield of TP was 96.5%under the described condition.Compared with traditional methods,including hot reflux extraction(HRE),ultrasound-assisted extraction(UAE)and supercritical fluid extraction(SFE),the extraction time was saved 8 times than that of HRE,and the yield was increased by 17.5%.The extraction time at comparable levels of production was saved 2 times,and the energy consumption was one fourth that of UAE.The extraction time was saved 5 times than that of SFE,and the yield of TP was increased by 40%.Moreover,compared with MAE of TP studied by others,it decreased the solid/liquid ratio from 1∶20 to 1∶12 g/mL without 90-min pre-leaching time,and the yield of TP was increased by 6%-40%.